1. Field of the Invention
This invention relates to a magneto-optical recording medium such as a magneto-optical disk on which erasing and rerecording are possible and which is used for a large-capacity information file or the like. This invention particularly relates to an improvement of a protective layer of the magneto-optical recording medium.
2. Description of the Prior Art
Optical recording media have various advantages. For example, they can record information at a high density, have a large capacity, and need not be contacted with a head. Among such media, the magneto-optical recording media have attracted special attention for enabling easy erasing and rerecording.
The magneto-optical recording medium is composed of a magnetic material as a recording medium, and records information based on changes in magnetization of the magnetic material. For example, an amorphous magnetic material composed of a combination of a rare earth metal (RE) such as Gd, Tb or Dy with a transition metal such as Fe, Co or Ni is used as the magnetic material. The magnetic material is used in a layer form as a recording layer. The magnetic material, particularly the rare earth metal contained therein, is readily oxidized. When the magnetic material is oxidized, magnetic characteristics such as the coercive force thereof deteriorate. Therefore, in order to isolate the recording layer from ambient air, the recording layer has heretofore been covered by a protective layer formed of a dielectric material.
The protective layer has heretofore been formed by a sputtering process or the like. However, the sputtering process has the drawback that free oxygen given rise to in the course of sputtering clings to the surface of the recording layer and penetrates through the recording layer, thereby oxidizing the magnetic material. Thus, ironically, oxidization is as a result promoted in the course of formation of the protective layer for the purpose of preventing oxidization.